Radiative cooling to subambient temperatures can be efficiently achieved through spectrally selective emission, which until now has only been realized by using complex nanoengineered structures. Here, a simple dip-coated planar polymer emitter derived from polysilazane, which exhibits strong selective emissivity in the atmospheric transparency window of 8–13 μm, is demonstrated. The 5 μm thin silicon oxycarbonitride coating has an emissivity of 0.86 in this spectral range because of alignment of the frequencies of bond vibrations arising from the polymer. Furthermore, atmospheric heat absorption is suppressed due to its low emissivity outside the atmospheric transparency window. The reported structure with the highly transparent polymer and underlying silver mirror reflects 97% of the incoming solar irradiation. A temperature reduction of 6.8 °C below ambient temperature was achieved by the structure under direct sunlight, yielding a cooling power of 93.7 W m–2. The structural simplicity, durability, easy applicability, and high selectivity make polysilazane a unique emitter for efficient prospective passive daytime radiative cooling structures.

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Nanostructured transparent conductive electrodes are highly interesting for efficient light management in thin-film solar cells, but they are often costly to manufacture and limited to small scales. This work reports on a low-cost and scalable bottom-up approach to fabricate nanostructured thin-film solar cells. A folded solar cell with increased optical absorber volume was deposited on honeycomb patterned zinc oxide nanostructures, fabricated in a combined process of nanosphere lithography and electrochemical deposition. The periodicity of the honeycomb pattern can be easily varied in the fabrication process, which allows structural optimization for different absorber materials. The implementation of this concept in amorphous silicon thin-film solar cells with only 100 nm absorber layer was demonstrated. The nanostructured solar cell showed approximately 10% increase in the short circuit current density compared to a cell on an optimized commercial textured reference electrode. The concept presented here is highly promising for low-cost industrial fabrication of nanostructured thin-film solar cells, since no sophisticated layer stacks or expensive techniques are required.

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